Field of the Invention
The present invention is generally related to levitating, suspending, moving, fluidizing, or mixing solid particles or fluid bubbles in a fluidic environment. More specifically, the present invention is related to an apparatus and method for levitating, suspending, moving, fluidizing, or mixing solid particles or fluid bubbles in a fluidic environment by suitable non-sinusoidal vibration.
Description of the Related Art
There are several existing methods for levitating or suspending particles in a fluid (liquid or gas). Levitation methods include using electromagnetic, electrostatic, acoustic, and aerodynamic forces. Electromagnetic and electrostatic methods can only levitate materials having the right electromagnetic properties and cannot levitate gas bubbles within a fluid. Acoustic levitation methods work with a wider range of material, but the material is only be levitated at specific acoustic nodes, and not dispersed throughout a volume. Aerodynamic levitation requires a net upwards directional flow of air or other fluid to keep particles suspended, and cannot simultaneously levitate gas bubbles and solid particles within a fluid.
The suspension of multiple particles in a fluid, also called fluidization, can also be achieved by vibration of a container or fluid at accelerations above gravity. When low frequency vibration is used, particles are imparted energy primarily through collisions with the bottom of the container or collisions with other particles. Ultrasonic vibrations transmit energy by sound waves through the bulk fluid which can accelerate particles and keep them suspended, or achieve a level of homogenization of a liquid that persists long after the vibrations ended. However, the energy required can be high if the particles are large or dense, and cavitation, which may be undesirable, often occurs.
Since the 1950s or earlier, it has been known that gas bubbles can be levitated in a liquid that is subjected to low frequency (about 100 Hz) vertical vibrations. The levitation is thought to be due in part to the bubble volume oscillating as it moves up and down within the liquid. The solutions to the force equations in the literature on this subject predict that a bubble will levitate at a certain height from the top of the liquid, depending on the oscillation frequency and other factors, but not the amplitude (as long as the amplitude of the acceleration is somewhat greater than the acceleration due to gravity). However, researchers have found that the amplitude of vibration does have some influence, though they have not yet explained why.
Prior researchers have made assumptions about the drag force acting on the air bubbles (or ignored drag altogether), leading to the erroneous conclusion that the drag force itself does not affect the levitation. However, drag forces acting on the bubbles can be complicated and are generally not linearly related to velocity. In particular, as the amplitude of vibration is increased, the maximum velocity of the bubbles can increase into the region where drag forces are more proportional to the square of the velocity. In other words, the bubbles had a high Reynolds number. Researchers have also not considered the effect of non-sinusoidal vibrations, possibly because they have assumed incorrectly that the response is linear.
The current general-purpose vibration testing procedures are single frequency tests, swept sine tests, random tests, and drop or impulse tests. These tests are insufficient to uncover significant defects (or features) which can be caused by non-linear vibration responses to some real-world non-sinusoidal vibrations. Vibration testing can be greatly improved by utilizing non-sinusoidal vibrations that enhances or exposes the non-linear vibration response. One particular industry that can greatly benefit from improved vibration testing is the aerospace industry, including battery systems, on-board fuel storage and delivery systems, and other multi-phase systems. The lack of adequate vibration testing has had severe results, resulting in aerospace disasters and costly grounding of aircraft.
Current devices and methods for the research or use of cavitation have a limited ability to control the strength or likelihood of cavitation independent of the other effects of vibration. Typically, an ultrasonic transducer driven with a single frequency is immersed in a fluid and the effects of sonication are concentrated near the surface of the transducer. Cavitation can be reduced or eliminated by reducing power or other parameters, reducing other desired effects of sonication. To achieve single bubble sonoluminescence, researchers commonly levitate and stabilize a single bubble via acoustic pressure standing waves which requires very specific driving frequencies. Another method developed more recently achieves stable sonoluminescence using a “water hammer tube” approximately half full with liquid. Driven externally with a single frequency, some bubbles are entrained and experience “negative” buoyancy, dropping to the bottom of the tube. This effect cannot be controlled without changing the frequency or amplitude of the vibrations, which affects the size and sonoluminescence of the bubbles.
Current devices for approximating the effects of microgravity under Earth gravity include drop towers, parabolic flights, and clinostats. Drop towers and parabolic flights only allow short periods of microgravity, up to about 20 seconds. Parabolic flights are expensive and limited to experiments that are safe to perform on an airplane. The best drop towers only give a period of about 10 seconds, with only a few repetitions possible per day, and high decelerations at the bottom limit the types of experiments that can be performed. Clinostats use rotation about a horizontal axis (or random rotation) so the time-averaged acceleration due to gravity is zero. Long experiments can be performed on clinostats, but this technique only works for items which respond slowly to acceleration, such as plants.
Current medical ultrasonography devices use a single frequency and measure the time and amplitude of echos to form an image inside the human body. Although generally considered safe, some studies have found weak, but statistically significant effects on children exposed to ultrasound in the womb. As a result, the FDA has established guidelines limiting the acoustic power using several metrics, primarily the Thermal Index (TI), which measures the potential for tissue heating, and the Mechanical Index (MI), which measures the risk of cavitation and, to a lesser degree, streaming.
Embodiments of the present invention include an apparatus and method to levitate, suspend, or mix particles or bubbles in a fluid, or to mix two or more fluids or granular materials, using of asymmetric vertical vibrations that nullify, reverse, or enhance the effect of gravity. Embodiments of the present invention can improve chemical reactions and other processes, and make new ones possible. Embodiments of the present invention can also be used to position particles or counteract the effect of residual acceleration in a microgravity environment. One embodiment of the present invention includes an apparatus and method for improved vibration testing. Another embodiment of the present invention is also an apparatus and method using vibration to improve batteries.